1. Field of the Invention
The present invention relates to a photographing optical system, and more particularly, to a compact photographing optical system used in electronic products.
2. Description of the Prior Art
The demand for compact imaging lens assembly has grown in recent years as the popularity of portable electronic products with the photographing function has increased. The sensor of a general photographing camera is none other than CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor Sensor). Furthermore, as advanced semiconductor manufacturing technology has allowed the pixel size of sensors to be reduced, and the current electronic products are leaning toward a trend of being more compact with more functionalities, there is an increasing demand for compact imaging lens assembly featuring better image quality.
A conventional compact imaging lens system equipped on a portable electronic product is often composed of three lens elements such as the lens system set forth in U.S. Pat. No. 7,184,225, comprising, in order from an object side to an image side: a first lens element with positive refractive power, a second lens element with positive refractive power and a third lens element with negative refractive power.
However, as the improved process technology and the trend of electronic products with compact appearance, the pixel size of sensors is getting smaller, and the demand for lens element featuring better image quality increases. Therefore, a conventional lens system with three lens elements can no longer satisfy photographing optical systems of even higher level.
A conventional compact imaging lens system equipped on a portable electronic product, such as the one set forth in U.S. Pat. No. 7,365,920, generally has a front stop and four lens elements; wherein, the first and second lens elements are adhered together to form a doublet for correcting the chromatic aberration. However, this kind of arrangement has the following disadvantages. First, the degree of freedom in arranging the lens system is curtailed due to the employment of excessive number of spherical glass lenses; thus, the total track length of the system cannot be reduced easily. Second, the process of adhering glass lenses together is complicated, posing difficulties in manufacturing. Moreover, as the size of imaging lens systems is becoming smaller and the specification thereof is becoming higher, assembling lens elements compactly within a limited space tend to cause unwanted light rays to reflect too many times within a lens barrel, which will affect image quality. Thus, in order to improve image quality, it would be beneficial to bar the unwanted light rays from entering the image forming area.
Inasmuch as the foregoing, a need exists in the art for a photographing optical system that features better image quality and is compact while maintaining a moderate total track length.